The present exemplary embodiments relate to discotic liquid crystalline porphyrins and discotic liquid crystalline porphyrin metal complexes. In certain embodiments, their homeotropically or homogenously aligned architecture, in which the columns formed by intermolecular stack are spontaneously perpendicular or parallel on the surface respectively, is a crucial point for their applications. They find use as high-efficiency photovoltaic materials, organic semiconducting materials, organic light emitting materials, materials for organic transistors and in solar cell device implementation. However, it is to be appreciated that the present exemplary embodiments are also amenable to other like applications.
In the long term, solar energy is the only source of renewable energy that has the capacity to fill humanity's technological needs. A grand challenge is to convert solar energy into green electric energy in an inexpensive and efficient way. Crystalline silicon photovoltaic cells, though efficient, are too expensive to compete with primary fossil energy. Organic photovoltaic (OPV) technology would hold the promise for cost reduction since the OPV materials are potentially cheap, easy to process, and capable of being deposited on flexible substrates such as plastics and bending, where their inorganic competitors e.g. crystalline silicon would crack.
New OPV materials able to efficiently absorb sunlight and new approaches based on nanostructured architectures holds the potential to revolutionize the technology used to produce solar electricity; however the availability of such new materials with tailored properties has undoubtedly posed a bottleneck to the OPV technology. A breakthrough of new material development is urgently needed to boost the feasibility and prevalence of OPV technology. Currently widely used OPV materials, e.g. polycrystalline Cu phthalocyanine, suffer from the scattering of electron/exciton between small crystal grain boundaries in which random arrangement of molecules results in poor charge mobility. The existing grain boundaries and defects act as deep traps that dramatically reduce the charge mobility. In addition, polycrystalline materials are intrinsically inhomogeneous. The attainment of large defect-free single crystals or single crystalline film of large area of either inorganic (e.g. silicon) or organic molecules is difficult and costly.
A challenge for OPV, with the possibility of very significant cost reduction, is to make them in desired macroscopic order to improve charge transportation etc. Discotic liquid crystals (LCs) capable of being homeotropically aligned (i.e. the columns formed by intermolecular strong stack are perpendicular to the electrode surface) would be a desirable candidate to meet the challenge since they can form ordered nanostructures at macroscopic scale for photovoltaic application. Unfortunately, the preferable homeotropic-alignment of discotic LCs, especially those having large conjugated systems, is difficult to achieve due to their high viscosity and poor affinity to substrates, as compared to the well established technologies for their calamitic counterparts in the display industry.
In order to make discotic LC with more efficient absorption of sunlight, one should consider porphyrin as the building block of the potentially most viable discotic material since it is the basic structure of the best photoreceptor in nature, chlorophyll. Porphyrin and its derivatives have many desirable features such as highly conjugated plane, high stability, intense absorption of sunlight, and the small gap between the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy level.
As will be described in detail, the present disclosure is an important extension of our previous application above. The materials described herein provide a broad range of discotic LCs capable of forming homeotropically/homogeneous aligned architecture. Chemical modifications can provide a way to control and improve their alignment which is a crucial point for their applications. The materials are capable of being used as photovoltaic materials, organic semiconductors and organic light emitting materials. Although the drawings, discussions and descriptions are mainly directed toward the preparation of the said materials, photovoltaic devices and methods, it is to be understood that the principles of the present invention are applicable to any type of devices that uses homeotropically or homogenously aligned architecture of any a discotic liquid crystal or the blend composed of a discotic liquid crystal and one or more other components as a layer.